Method for manufacturing connected sheet material, connected sheet material and method for manufacturing optical display unit

ABSTRACT

The invention is to provide a process for production of a connected sheet product, which makes it possible to connect opposed end faces of two or more sheet products. A process for production of a connected sheet product including sheet products that are connected to one another and each have at least an optical member and a release film provided on one side of the optical member with a pressure-sensitive adhesive interposed therebetween, comprising: opposing a transverse end face of a first sheet product to a transverse end face of a second sheet product; connecting release films of the first and second sheet products with a connecting member ( 30   a ); and connecting surface members of the first and second sheet products with a connecting member ( 30   b ) on the opposite side from the release films.

TECHNICAL FIELD

The invention relates to a process for production of a connected sheetproduct by connecting the end faces of sheet products to each other, andto such a connected sheet product. The invention also relates to aprocess for production of an optical display unit with such a connectedsheet product.

BACKGROUND ART

A description is given below of a manufacturing method including bondingan optical film to an optical display unit (such as a glass substrateunit in which a liquid crystal is sealed). First, a material roll of along sheet product including an optical film member is manufactured. Forexample, the “long sheet product” includes a raw material for apolarizing plate for use in a liquid crystal display. For example, aroll of a raw material for a polarizing plate is manufactured by theprocess described below. The upstream process includes (A) the step ofobtaining a polarizer; (B) the step of manufacturing a polarizing plate,which includes placing a polarizer protecting film on one or both sidesof the polarizer with an adhesive interposed therebetween and drying thelaminate to give a polarizing plate; and (C) the step of bonding arelease film (also called “separator”) and a surface protecting film. Inthe upstream process, a long sheet product is manufactured, wound into aroll and subjected to the downstream process.

(D) The step of slitting the material roll is performed, in which sincethe material roll is wide, the material is slit into a predeterminedsize depending on the size of an optical display unit (the finalproduct). As mentioned above, the long sheet product is manufactured inthe form of a material roll. When the long polarizing plate is drawnfrom the resulting material roll and subjected to processing, continuoussupply from the roll is made possible by a method that includes joiningthe material to the next roll, when the remaining length of the materialof the roll becomes small, and feeding the material. Conventionalexamples of the joining method (also referred to as “splicing method”)include methods as shown in parts (a) and (b) of FIG. 7, which includelayering an end portion of a sheet product 701 and an end portion ofanother sheet product 702 and bonding them by fusion or with an adhesivetape. FIG. 7 is a cross-sectional view of the connected portion betweenthe sheet products.

The process may also include continuously feeding the sheet product fromthe roll, peeling off only the separator, and automatically inspectingany defect in the polarizing plate. In this case, if the process isstopped for every material roll, the work efficiency will be reduced.Therefore, it is proposed that an end portion of the sheet product beinginspected should be connected to an end portion of the next sheetproduct. However, when the end portions are layered and connected asmentioned above, it is impossible to peel off only the separator.

Next, a description is given of the step of bonding an opticalmember-containing sheet product to a substrate as a component of anoptical display unit. For example, Patent Literature 1 (Japanese PatentApplication Laid-Open (JP-A) No. 2007-140046) discloses a processincluding unwinding and feeding a belt-shaped sheet product from a rollof the sheet product, detecting any defect in the sheet product, cuttingthe sheet product into individual pieces based on the result of thedetection, and bonding each cut piece to a substrate, wherein in thebonding, only the separator is peeled off from the sheet product, andthen the sheet product is bonded to the substrate with the remainingpressure-sensitive adhesive interposed therebetween.

Alternatively, another proposed method includes cutting members otherthan the separator (the polarizing plate and the surface protectingfilm), while keeping the separator continuous, and bonding the sheetproduct to a substrate with the remaining pressure-sensitive adhesiveinterposed therebetween, while peeling off only the separator. In orderto perform the bonding process continuously, the sheet product beingsupplied needs to be connected to the next sheet product as mentionedabove. Also in this case, if the end portions of the sheet products arelayered and connected as mentioned above, it is impossible to peel offonly the separator.

Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No.2007-140046

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

The invention has been made in view of the above circumstances, and anobject of the invention is to provide a process for production of aconnected sheet product, which makes it possible to connect opposed endfaces of two or more sheet products; and to provide such a connectedsheet product and a process for production of an optical display unit.

Means for Solving the Problems

The invention is directed to a process for production of a connectedsheet product including sheet products that are connected to one anotherand each include at least an optical member and a release film providedon one side of the optical member with a pressure-sensitive adhesiveinterposed therebetween, which includes:

opposing a transverse end face of a first sheet product to a transverseend face of a second sheet product;

connecting release films of the first and second sheet products with aconnecting member; and

connecting surface members of the first and second sheet products with aconnecting member on the opposite side from the release films.

The process is effective and advantageous as described below. The sheetproduct includes at least an optical member and a release film providedon one side of the optical member with a pressure-sensitive adhesiveinterposed therebetween. The optical member may be typically, but notlimited to, any of various optical films having a monolayer structure ora laminated structure. The thickness of the optical member may typicallybe from 5 μm to 500 μm, while it depends on the structure of the opticalmember. Examples of an optical film include a polarizing plate, aretardation plate, a brightness enhancement film, and a light diffusionplate. The optical member may include an optical film and any other filmplaced thereon. For example, such any other film may be a polarizerprotecting film for protecting a polarizer, a surface protecting memberor a release film provided on the surface of the outermost layer, or thelike. The surface protecting member is preferably in the form of a film.When the optical member has a laminated structure, the respective layersmay typically be provided with an adhesive, a pressure-sensitiveadhesive or the like interposed between them. A laminated film formed bya coextrusion process may also be used as a component to form theoptical member. The optical member is preferably a polarizing plate or alaminated structure including a polarizing plate. For example, thepolarizing plate may include a stretched and dyed polyvinyl alcohol filmpolarizer and a polarizer protecting film that is provided on at leastone side of the polarizer with an adhesive interposed therebetween andtypically includes a triacetylcellulose film.

For example, the pressure-sensitive adhesive may be a rubber-basedpressure-sensitive adhesive, an acrylic pressure-sensitive adhesive, asilicone pressure-sensitive adhesive, an epoxy pressure-sensitiveadhesive, or a cellulose pressure-sensitive adhesive. An acrylicpressure-sensitive adhesive with a high level of heat resistance ortransparency is preferred. The pressure-sensitive adhesive preferablyforms a layer, and the thickness of such a layer is typically from 1 to50 μm.

An acrylic pressure-sensitive adhesive is generally obtained bypolymerization of a main monomer for imparting adherability, a comonomerfor imparting cohesiveness, and a functionality-containing monomer forimparting adherability and forming a crosslinking point. Such an acrylicpressure-sensitive adhesive preferably has a glass transitiontemperature of −60° C. to −10° C., a weight average molecular weight of200,000 to 2,000,000, and a refractive index of 1.45 to 1.65. Under theconditions described above, a practically sufficient adhesive strengthis obtained for long-term attachment to a liquid crystal cell. Forexample, an acrylic pressure-sensitive adhesive having the aboveproperties may be produced by reference to Katsuhiko Nakano,“Secchaku/Nenchaku no Kagaku to Oyo (Chemistry and Applications ofAdhesion/Pressure-Sensitive Adhesion),” published in Japanese byDainippon tosho Co., Ltd.

The material and the thickness of the release film are not restricted,and any of various films may be used as the release film. For example,the release film may be a polyethylene terephthalate (PET) film, apolyethylene (PE) film, a polypropylene (PP) film, or the like. Forexample, the thickness of such a film may be in the range of 12 μm to 80μm.

The sheet products used to form the connected sheet product are notlimited to two sheet products. For example, two or more sheet productsmay be connected in series to form the connected sheet product. Thefirst sheet product used to form the connected sheet product and thesecond sheet product to be connected to the first sheet product may bethe same or different in longitudinal length. In an embodiment of theinvention, the “longitudinal length” of the sheet product is preferablyten times or more the transverse length perpendicular thereto. The twoor more sheet products to be connected may include the same membercomponents or different member components.

The connecting method includes opposing the transverse end face of thefirst sheet product to the transverse end face of the second sheetproduct, connecting the release films of the first and second sheetproducts with a connecting member, and connecting the surface members ofthe sheet products with a connecting member on the opposite side fromthe release films. As used herein, the term “oppose” means that the endfaces of the sheet products are placed with a gap of, for example, 0.1mm to 20 mm between them or without any gap between them, while there isno overlap between the sheet products. When the end faces of the firstand second sheet products are opposed to each other, the end face linesare preferably parallel to each other. Before the connecting step,therefore, the end face portion of the first or second sheet product maybe cut parallel to the transverse direction of the sheet product.

The release films of the first and second sheet products are connectedto each other with a connecting member. On the opposite side from therelease films, the surface members of the sheet products are connectedto each other with a connecting member. The surface member of the sheetproduct may correspond to the uppermost component of the optical member,examples of which include a surface protecting member, a polarizerprotecting film, and so on.

For example, the connecting member may be an adhesive tape or the like.For example, a connecting method may include opposing the end faces ofthe first and second sheet products to each other and pressing a heatsealing tool directly against the surfaces of the opposed sheet portionsto join the surfaces of the sheet portions by heat fusion. In this case,the sheet surface member produced through melting and solidificationcorresponds to the connecting member (see FIG. 3). In the connectingstep, a single connecting member is preferably used, and it is morepreferably an adhesive tape. It is because when such an adhesive tape isused, the connecting method can be completed in a short time even byhand. The connecting member is preferably placed over the wholetransverse length of the sheet products.

Examples of the adhesive tape include a pressure-sensitiveadhesive-impregnated nonwoven fabric, a product composed of a backing ofpolypropylene or the like and a pressure-sensitive adhesive coatingprovided thereon, and so on. The adhesive tape preferably has athickness in the range of 10 μm to 5 mm and an adhesive strength in therange of 1 N/25 mm to 30 N/25 mm. The adhesive strength may be tested bythe 180 degree peel test according to JIS Z 0237 (1991). In this case,the sheet product is used to form the test plate (adherend). Inaddition, the adhesive tape preferably has a tensile strength of 100N/25 mm or more and an elongation percentage of 200% or less. Thetensile strength may be tested by the method according to JIS Z 0237(1991). Under the conditions described above, the adhesive tape has norisk of breaking, even when the working operation for joining the sheetproducts is continuously performed.

The joining operation may be performed by hand. Alternatively, forexample, the joining operation may be performed using a dedicatedapparatus such as a bonding roll. For example, the bonding roll may havesuch a structure that a roll core is coated with a rubber layer with athickness of about several to several tens of millimeters.

In the connecting process, the steps of connecting the release films ofthe first and second sheet products and connecting the surface membersof the sheet products on the opposite side from the release films may beperformed in any order or in parallel.

When the connected sheet product is obtained by the production methoddescribed above, for example, the sheet products can be continuouslyprocessed without stopping the production line. Therefore, it has highproductivity. The structure of the connected sheet product makes itpossible to smoothly peel off the release film placed on thepressure-sensitive adhesive without interference with other constituentmembers. In the process of peeling off the release film, the first andsecond sheet products are kept connected by the connecting member, whichconnects the surface members of the sheet products. Therefore, when thesheet product, from which the release film is peeled off, is attached tothe desired object with the pressure-sensitive adhesive interposedtherebetween, the continuous operation can be successfully retained, andthe trouble with the continuous production can be significantly reduced.

The features described below should be satisfied in order that therelease films may be continuously and smoothly peeled off withoutbreaking at the connected portion. The release films 12 and 22 may bepeeled off in the direction shown in the FIG. 2. In this case, therelation C≧A>B (formula 1) should be satisfied, wherein A represents theadhering force between the connecting member 30 b and the release film22 of the second sheet product 2 (at the portion indicated by an ellipsea), B represents the adhering force between the release film 22 of thesecond sheet product 2 and the pressure-sensitive adhesive layer 22 a(at the portion indicated by an ellipse b), and C represents theadhering force between the connecting member 30 a and the surfaceprotecting film 23 of the second sheet product 2 (at the portionindicated by an ellipse c).

The adhering forces may be measured by the adhesive strength test methoddescribed above. The adhering forces A and C are each preferably tentimes or more greater than the adhering force B. When sheet productseach with a width size of 1,300 mm or more are connected, the adheringforces A and C are each preferably 100 times or more (e.g., 100 to 300times) the adhering force B. Concerning the adhering forces A, B and C,the adhering force B may be first determined according to the structureof the sheet product, and therefore, the adhering forces A and C may beappropriately determined by appropriately changing the connectingmembers. For example, the sheet product may be a laminated structureincluding a surface-protecting polyethylene terephthalate film, anacrylic pressure-sensitive adhesive layer, a polarizing plate, anotheracrylic pressure-sensitive adhesive, and a silicone-treated polyethyleneterephthalate release film. In such a case, the adhering force B (peelforce) between the acrylic pressure-sensitive adhesive layer and thesilicone-treated polyethylene terephthalate film is generally from 0.005N/25 mm to 0.1 N/25 mm. In this case, the connecting members to be usedare preferably such that the adhering force A to the release film andthe adhering force C to the surface protecting film can each be 10 timesor more the adhering force B. In addition, the adhering force betweenthe pressure-sensitive adhesive layer 22 a and the polarizing plate 21and the adhering force between the polarizing plate 22 and the surfaceprotecting film 23 through the pressure-sensitive adhesive layer 23 ashould each be equal to or greater than the adhering force A between theconnecting member 30 b and the release film 22 of the second sheetproduct 2.

Another embodiment of the invention is directed to a connected sheetproduct, including:

first and second sheet products that are connected to each other andeach include at least an optical member and a release film provided onone side of the optical member with a pressure-sensitive adhesiveinterposed therebetween, wherein a transverse end face of the firstsheet product and a transverse end face of the second sheet product areopposed to each other;

a connecting member with which the release films of the first and secondsheet products are connected to each other; and

another connecting member with which surface members of the first andsecond sheet products are connected to each other on the opposite sidefrom the release films.

This structure is effective and advantageous, as is the connected sheetproduct manufactured by the above method of production of the connectedsheet product.

Another embodiment of the invention is directed to a process forproduction of an optical display unit, including:

a cutting step for cutting the above connected sheet product or theconnected sheet product manufactured by the method of manufacture of theconnected sheet product with exception of a release film into a piecewith a predetermined size by cutting means; and

a bonding step for bonding the piece with the predetermined size to asubstrate with the pressure-sensitive adhesive interposed therebetweenwhile removing the release film.

The process is effective and advantageous as described below. While theconnected sheet product may be manufactured in advance, the opticaldisplay unit production process preferably includes producing theconnected sheet product. A first material roll including a roll of afirst long sheet product may be placed, from which the first sheetproduct may be fed to the downstream process. The first sheet productother than the release film may be cut into a predetermined size usingcutting means (cutting step). The cut piece of the first sheet productmay then be bonded to a substrate with the pressure-sensitive adhesiveinterposed therebetween while the release film is removed (bondingstep). Any additional step may be performed between the cutting step andthe bonding step. In the above steps being continuously performed, asecond sheet product needs to be subsequently connected to the firstsheet product being supplied, in order to continuously supply the firstsheet product. In this process, the connecting method to be usedincludes: opposing a transverse end face of the first sheet product to atransverse end face of the second sheet product; connecting the releasefilms of the first and second sheet products with a connecting member;and connecting surface members of the sheet products with a connectingmember on the opposite side from the release films. Hereinafter, theconnecting step is also referred to as “splicing step.” The first orsecond sheet product may also be a connected sheet product previouslymanufactured by connecting two or more sheet products by the sameconnecting method as described above.

As described above, the sheet products are connected without beingoverlapped with each other, so that only the release film can be peeledoff in a continuous process. In addition, the connecting member canprovide a sufficient adhering force, so that the connected portion canbe prevented from breaking during the feeding. Therefore, the cuttingstep and the bonding step can be continuously performed, so that theoptical display unit can be manufactured with significantly improvedproductivity.

The manufacturing process described above may further include the stepsof removing the release film (a first release film removing step),inspecting any defect (a defect inspecting step), and bonding a releasefilm to the sheet product with the pressure-sensitive adhesiveinterposed therebetween (a second release film bonding step).

In the defect inspection, any defect in the optical film can beinspected, regardless of whether the release film has any defect such asretardation existing in the release film and foreign matter or scratchesadhering to or existing in the release film. The release film to beattached again to the sheet product may be a used or new one. In orderthat the release film to be attached again to the sheet product may becontinuously supplied, the process preferably includes opposing thetransverse end faces of release films to each other and joining, with ajoining member, the opposite surfaces of the release films from thesurfaces to be attached to the sheet product. This process makes itpossible to continuously peel off only the release film attached againto the sheet product.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for illustrating a connecting method;

FIG. 2 is a schematic diagram showing a process of peeling off releasefilms;

FIG. 3 is a schematic diagram for illustrating another connectingmethod;

FIG. 4 is a flow chart of a process for production of an optical displayunit;

FIG. 5 is a flow chart of another process for production of an opticaldisplay unit;

FIG. 6 is a diagram for illustrating the configuration of a productionsystem according to the invention; and

FIG. 7 is a diagram for illustrating conventional connecting methods.

DESCRIPTION OF REFERENCE CHARACTERS

In the drawings, reference character 1 represents a first sheet product,2 a second sheet product, 11 a polarizing plate, 12 a release film, 12 aa second pressure-sensitive adhesive, 13 a surface protecting film, 13 aa first pressure-sensitive adhesive, and 30 a and 30 b each a connectingmember.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the connecting method of the invention are describedbelow. Now, a description is given of a method for connecting first andsecond sheet products. FIG. 1 shows the procedure of a connectingmethod. FIG. 2 is a diagram illustrating a process of peeling offrelease films. Each of the first and second sheet products 1 and 2, forthe description below, is, but not limited to, a laminated structureincluding a surface protecting film 13 or 23, a first pressure-sensitiveadhesive 13 a or 23 a, a polarizing plate 11 or 21, a secondpressure-sensitive adhesive 12 a or 22 a, and a release film 12 or 22.Part (a) of FIG. 1 is a cross-sectional view of a connected portionwhere the first and second sheet products are connected. Part (b) ofFIG. 1 is a plan view of the connected portion where the first andsecond sheet products are connected.

(1) Opposing Step (FIG. 1). The transverse end faces of the first andsecond sheet products 1 and 2 are opposed face-to-face. While the gapbetween the end faces is preferably as small as possible, an importantthing in this step is that they must be opposed to each other with nooverlap between them. The end faces are preferably parallel to eachother. To keep the opposed end faces parallel to each other, a measuringinstrument for measuring the parallel state and a tool for fixing thesheet products, such as suction means, may be used in the step ofopposing the end faces of the sheet products.

(2) Connecting Steps (FIG. 1). On the respective surface sides, therelease films 12 and 22 of the first and second sheet products 1 and 2and the surface protecting films 13 and 23 of the first and second sheetproducts 1 and 2 are then connected with connecting members 30 b and 30a, respectively. The connecting members to be used may be, but notlimited to, adhesive tapes. As shown in part (b) of FIG. 1, theconnecting members 30 a and 30 b are each attached to substantially thewhole transverse length of the first and second sheet products. Forexample, the lengths X1 and X2 of the portions where the connectingmember 30 a is bonded to the first and second sheet products 1 and 2,respectively, are preferably 10 mm or more from the end faces of thefirst and second sheet products 1 and 2, respectively.

This process makes it possible to oppose and join the end faces of thetwo sheet products with no overlap between the two sheet products. Theconnecting members can each provide a sufficient adhering force, andtherefore, the connected portion can be prevented from breaking duringthe feeding. In addition, even when only the release films arecontinuously peeled off, the connecting member on the other side cankeep the first and second sheet products connected together.

Process for Production of Connected Sheet Product

The method of the invention for producing a connected sheet product isdescribed below. In the description, a laminate of a surface protectingfilm, a polarizing plate, and a release film is used as an example ofthe structure of the sheet product. The release film is provided on thepolarizing plate with a pressure-sensitive adhesive interposedtherebetween. The polarizing plate includes a polarizer and polarizerprotecting films provided on both sides of the polarizer.

(1) Step of Obtaining Polarizer. In this step, a polyvinyl alcohol (PVA)film is dyed, crosslinked, stretched, and dried to give a polarizer. (2)Step of Producing Polarizing Plate. In this step, polarizer protectingfilms are placed on both sides of the polarizer with an adhesiveinterposed therebetween, and the resulting laminate is dried to give apolarizing plate. The polarizer protecting films bonded to both sidesmay have the same or different compositions. The polarizer protectingfilm to be placed on the viewer side of a display may have beenpreviously subjected to an antiglare treatment.

(3) Step of Bonding Release Film and Surface Protecting Film. A releasefilm is bonded to one side of the polarizing plate with a strongpressure-sensitive adhesive interposed therebetween, and a surfaceprotecting film is bonded to the other side of the polarizing plate witha weak pressure-sensitive adhesive interposed therebetween. In thisprocess, the release film and the surface protecting film have beenpreviously coated with the strong pressure-sensitive adhesive and theweak pressure-sensitive adhesive, respectively. After the release filmis peeled off, the strong pressure-sensitive adhesive, which has beenapplied to the release film, is transferred to the polarizer protectingfilm. Even when the surface protecting film is peeled off, the weakpressure-sensitive adhesive, which has been applied to the surfaceprotecting film, still remains on the surface protecting film and issubstantially not transferred to the polarizer protecting film. In thesteps (1) to (3), a long sheet product is manufactured and wound into aroll, which is subjected to the next step. (4) Step of Slitting MaterialRoll. Since the material roll is wide, the material is slit into apredetermined size depending on the size of the final product, anoptical display unit. Optionally, a specific check may be performed by achecker in each of the above steps, or various automatic inspections(such as known defect inspections) may be performed with inspectionsystems.

(5) The step of peeling off the release film from the long sheet productobtained by slitting is performed (peeling step). For example, this stepis necessary when a defect inspection is performed on the sheet productwith the release film peeled off. In another case, the release film hasto be peeled off, when it needs to be replaced with another one. Inthese cases, if the first and second sheet products need to becontinuously subjected to the process, the first and second sheetproducts must be connected. In these cases, the connecting methoddescribed above is preferably used in the process of connecting thefirst and second sheet products. The method makes it possible to opposeand join the end faces of the two sheet products with no overlap betweenthe two sheet products.

Alternatively, without the above peeling step, the first and secondsheet products may be properly connected using the above connectingmethod, so that a single material roll can be formed. For example, whenthe full length of the first sheet product is less than the desiredlength, the first and second sheet products may be joined to form amaterial roll.

Method for Manufacturing Optical Display Unit

Next, a method for manufacturing an optical display unit is describedbelow. FIG. 7 shows a flow chart of a method for manufacturing anoptical display unit.

(1) Step of Providing Material Roll (S41 in FIG. 4). A first roll of afirst long sheet product is provided. In the description, a laminate ofa surface protecting film, a polarizing plate and a release film is usedas an example of the structure of the sheet products (the first andsecond sheet products). The release film is provided on one side of thepolarizing plate with a pressure-sensitive adhesive interposedtherebetween, and the surface protecting film is provided on the otherside of the polarizing plate with a pressure-sensitive adhesiveinterposed therebetween. The polarizing plate includes a polarizer andpolarizer protecting films provided on both sides of the polarizer. Eachpressure-sensitive adhesive forms a layer.

(2) Feeding Step (S42 in FIG. 4). The first sheet product is fed fromthe first material roll to the downstream process. The feeding mechanismof the feeding means may include known means, and for example, the sheetproduct may be inserted between a pair of rolls and fed by the rotaryaction of the pair of rolls.

(3) Cutting Step (S43 in FIG. 4)

The first sheet product fed from the feeding means is then partially cutby cutting means so that constituent members of the first sheet productother than the release film can be cut into a predetermined size.Therefore, other members of the first sheet product 1 including thesurface protecting film, the pressure-sensitive adhesive, the polarizingplate, and the pressure-sensitive adhesive may be cut without therelease film being cut. For example, the cutting means may be a laser, acutter or any other known cutting means.

(4) Bonding Step (S44 in FIG. 4). After the cutting step, the cut pieceof the first sheet product with the release film being removed is thenbonded to a substrate with the pressure-sensitive adhesive interposedtherebetween. For example, the substrate may be a glass substrate of aliquid crystal cell, an organic EL emitter substrate, or the like. In apreferred mode, the substrate has been previously cleaned before thebonding step.

The respective steps are performed in a continuous production line. Theprocess also includes a splicing step that includes connecting the endface of the first sheet product to the end face of the second sheetproduct so that the process can be continuously performed even when thematerial is changed to the second sheet product. The connecting methoddescribed above is preferably used in this splicing step.

In the series of manufacturing steps, the first sheet product is bondedto one side of the substrate. Another sheet product may also be bondedto the other side by the same bonding process as described above.

(5) The production process also preferably includes an inspecting step(FIG. 4). Examples of the inspecting step include the step of inspectingthe bonded state and the step of inspecting any defect after thebonding. Both inspections are preferably performed, while any one of theinspections may be performed.

(6) The substrate determined as non-defective in the inspecting step isused to form an optical display device (mounting step). When it isdetermined as defective, it is subjected to a reworking process in whicha new optical film is bonded and then inspected, and when the product isdetermined as non-defective, it is subjected to the mounting step, butwhen the product is determined as defective, it is subjected to thereworking process again or discarded.

Skip Cutting Method

Another mode of the cutting step is described below. Information aboutdefects the first sheet product (such as coordinates of defects, defecttype, and defect size) may be attached as coded information (e.g., QRcode or bar code) to one transverse end portion of the first materialroll per specific pitch unit (e.g., 1,000 mm). In such a case, the codedinformation may be read and analyzed at a stage before cutting, and thenin the first cutting step, the product may be cut into a predeterminedsize so that the defects can be separated (this process is also referredto as skip cutting). The system may be configured so that thedefect-containing portion can be rejected or bonded to a certain memberother than the substrate and that the cut piece of the sheet producthaving the predetermined size and determined as non-defective can bebonded to the substrate. This process significantly improves the yieldof the optical display unit.

Another Embodiment

Another Method for Manufacturing Optical Display Unit

Next, another method for manufacturing an optical display unit isdescribed below. FIG. 5 shows a flow chart of another method formanufacturing an optical display unit. In the description, the same stepas that in the above manufacturing method is briefly described oromitted.

(1) Step of Providing First Material Roll (S51 in FIG. 5). A firstmaterial roll of a first long sheet product is provided. The structureof the sheet product (the first or second sheet product) is the same asdescribed above.

(2) Feeding Step (S52 in FIG. 5). After the step of providing thematerial roll, the first sheet product is fed from the material roll tothe downstream process (feeding step).

(3) Step of Removing First Release Film (S53 in FIG. 5). The firstrelease film is removed from the first sheet product being fed. Examplesof a method for removing the first release film include a methodincluding continuously separating the film, while winding the separatedfilm on a roll, a method including cutting only the first release filminto units with a predetermined size and peeling off and removing eachunit with a pressure-sensitive adhesive tape, and a removing methodincluding any other process.

(4) Defect Inspecting Step (S54 in FIG. 5). After the step of removingthe first release film, defect inspection is performed. In this case,the defect inspection can be performed on the optical film, regardlessof whether the first release film has a retardation. The defectinspection may be performed using known methods.

(5) Step of Bonding Second Release Film (S55 in FIG. 5). After thedefect inspecting step, a second release film is bonded to the firstsheet product with the pressure-sensitive adhesive interposedtherebetween. To maintain the flatness, it is preferred that the bondingstep should be performed so that bubbles such as air bubbles may not betrapped.

(6) Cutting Step (S56 in FIG. 5). The first sheet product fed from thefeeding means is then partially cut by cutting means so that constituentmembers of the first sheet product other than the second release filmcan be cut into a predetermined size.

(7) Bonding Step (S57 in FIG. 5). After the cutting step, the firstsheet product with the second release film being removed is bonded to asubstrate with the pressure-sensitive adhesive interposed therebetween.

The respective steps are performed in a continuous production line. Theprocess also includes a splicing step that includes connecting the endface of the first sheet product to the end face of the second sheetproduct so that the process can be continuously performed even when thematerial is changed to the second sheet product. The connecting methoddescribed above is preferably used in this splicing step.

In the series of manufacturing steps, the first sheet product is bondedto one side of the substrate. Another sheet product may also be bondedto the other side by the same bonding process as described above. Theinspecting step (FIG. 5), the mounting step and so on are the same asthose described above.

Preferred Manufacturing System for Performing the Optical Display UnitManufacturing Method

A preferred manufacturing system for performing the above other opticaldisplay unit manufacturing method is described below. FIG. 6schematically shows the configuration of the manufacturing system.

As shown in FIG. 6, the manufacturing system includes: a firstmanufacturing unit for bonding the first sheet product 1 to thesubstrate and a second manufacturing unit for bonding the second sheetproduct to the surface of the substrate other than the substrate surfaceto which the first sheet product is bonded. The first and second sheetproducts each have the same structure as that of the sheet product inFIG. 1.

The first manufacturing unit includes: mounting means on which the firstmaterial roll of the first long sheet product 1 is mounted; feedingmeans for feeding the first sheet product 1 from the first materialroll; first release film-removing means for removing the first releasefilm from the first sheet product 1 being fed; defect inspecting meansfor performing defect inspection after the removal of the first releasefilm; second release film-bonding means for bonding a second releasefilm to the first sheet product 1 with the pressure-sensitive adhesiveinterposed therebetween after the first defect inspection; cutting meansfor cutting the first sheet product 1 into a predetermined size withoutcutting the second release film after the bonding of the second releasefilm; bonding means for bonding the first sheet product, from which thesecond release film is being removed, to the substrate with thepressure-sensitive adhesive interposed therebetween after the cutting;and first control means for synchronizing and controlling the respectivemeans.

The second manufacturing unit includes: mounting means on which thesecond material roll of the second long sheet product is mounted;feeding means for feeding the second sheet product from the secondmaterial roll; third release film-removing means for removing the thirdrelease film from the second sheet product being fed; second defectinspecting means for performing defect inspection after the removal ofthe third release film; fourth release film-bonding means for bonding afourth release film to the second sheet product with thepressure-sensitive adhesive interposed therebetween after the seconddefect inspection; cutting means for cutting the second sheet productinto a predetermined size without cutting the fourth release film afterthe bonding of the fourth release film; bonding means for bonding thesecond sheet product, from which the fourth release film is beingremoved, to the surface of the substrate other than the substratesurface to which the first sheet product is bonded, with thepressure-sensitive adhesive interposed therebetween after the cutting;and second control means for synchronizing and controlling therespective means.

The first and second manufacturing units may be each independentlydriven or driven in a synchronized manner. The first and second controlmeans may be used to drive and control the series of steps in asynchronized manner. The release film removing means, the defectinspecting means, or the release film bonding means may be omitted fromthe system.

First Manufacturing Unit

Mounting means 301 includes a roll mount apparatus on which the firstmaterial roll of the first long sheet product 1 is mounted and which isgeared to a motor or the like to rotate freely or at a certain speed.The first control means controls the rotational speed and the driving.

Feeding means 302 feeds the first sheet product 1 from the firstmaterial roll and to each step. A tension controller is placed at a keypoint in each step. The feeding means 302 is controlled by the firstcontrol means.

The first release film-removing means is configured to delaminate andremove the first release film from the first sheet product 1 being fedand to wind it into a roll. The speed of winding it into the roll iscontrolled by the first control means. The delaminating mechanism has asharp-ended knife edge and is configured so that the first release filmcan be delaminated and removed by taking up the first release film withthe knife edge and turning the direction of the feeding and that thefirst sheet product 1 separated from the first release film can be fedin the feeding direction.

Defect inspecting means 303 inspects defects after the removal of thefirst release film. The defect inspecting means 303 includes a CCDcamera or a CMOS camera, and the image data taken by it are sent to thefirst control means. The first control means analyzes the image data todetect defects and calculates their position coordinates. The defectposition coordinates are used in the skip cutting process with thecutting means described below.

Second release film-bonding means bonds a second release film to thefirst sheet product with the pressure-sensitive adhesive interposedtherebetween after the defect inspection. As shown in FIG. 6, the secondrelease film is unwound from a material roll of the second release film,and the second release film and the first sheet product are insertedbetween one or more pairs of rollers so that they are bonded to eachother under a certain pressure from the pair of rollers. The rotationalspeed of the pair of rollers, the pressure, and the feeding arecontrolled by the first control means.

Cutting means 304 cuts the first sheet product 1 into a predeterminedsize without cutting the second release film after the bonding of thesecond release film. The cutting means 304 is a laser system. Based onthe defect position coordinates detected by the defect inspection, thecutting means 304 cuts the product into the predetermined size in such amanner that defective portions can be separated. Therefore, cut pieceshaving any defective portion are rejected as defective in a later step.Alternatively, the cutting means 304 may ignore defective portions andcontinuously cut the product into the predetermined size. In this case,the bonding process may be designed not to bond, but to remove thedefective portion or to bond the defective portion to a temporary plateunit, as described below. In this case, the first control means may alsofunction to control the process.

The cutting means 304 also includes a holding table placed to adsorb andhold the first sheet product 1 from the back side, and the laser systemis placed above the first sheet product 1. The laser system is moved inthe horizontal direction to scan the first sheet product 1 in the widthdirection, so that the first sheet product is cut at a predeterminedpitch in the feeding direction, while the second release film at thebottom is left uncut. This cutting technique is also referred to as“half cutting.” In the laser system, an air nozzle for blowing a warmwind to the portion being cut and a smoke collecting duct for collectinggas (smoke) generated from the portion being cut and carried by the warmwind are preferably configured in combination and placed opposite toeach other across the width of the first sheet product 1. The feedingmechanism includes step rollers 302 a and 302 b provided verticallymovable upward and downward so that continuous feeding of the firstsheet product 1 can be prevented from being stopped on the upstream anddownstream sides when the holding table adsorbs the first sheet product1. This operation is also controlled by the first control means.

After the cutting process, bonding means bonds the first sheet product 1(from which the second release film has been removed) to the substrate Wwith a pressure-sensitive adhesive interposed therebetween, while itremoves the second release film. In the bonding process, a press roller305 is used to press the first sheet product 1 against the surface ofthe substrate W so that it can be bonded to the surface. The pressureand movement of the press roller 305 are controlled by the first controlmeans. The delamination mechanism has a sharp-ended knife edge and isconfigured so that the second release film can be peeled off by takingup the second release film with the knife edge and turning the directionof the feeding and that the first sheet product 1 peeled off from thesecond release film can be fed to the surface of the substrate W. Thisprocess may include applying a tension of 150 N/m to 1,000 N/m to thesecond release film and/or pressing the first sheet product against thesurface of the substrate W within 3 seconds from the removal of thesecond release film, so that the first sheet product 1 can be bondedwith improved accuracy. If the tension is less than 150 N/m, theposition from which the first sheet product is fed may be unstable. Ifit is more than 1,000 N/m, the second release film may be elongated tobreak. If the time until the pressing is longer than 3 seconds, the endportion of the first sheet product peeled off from the second releasefilm may be bent so that folding or air bubbles may occur. The bondingmechanism includes the press roller 305 and a guide roller opposedthereto. The guide roller includes a rubber roller driven by a motor,and immediately above the guide roller, the press roller 305 comprisinga metallic roller driven by a motor is provided movable upward anddownward. When the substrate W is fed to the bonding position, the pressroller 305 is elevated to a position higher than the upper surface sothat the space between the rollers is widened. Alternatively, the guideroller and the press roller 305 may each be a rubber roller or ametallic roller. The substrate W has been previously cleaned by cleaningmeans and stored in a storing unit. It is placed on the feedingmechanism by suction feeding means 306, which is also controlled by thefirst control means.

Second Manufacturing Unit

The substrate W1 fed from the first manufacturing unit is turned upsidedown in the feeding process or in the second manufacturing unit. Theturning means (not shown) is configured to suck the substrate W1 fromthe upper side by sucking means, lift it, turn it upside down, and placeit the feeding mechanism again. The second control means functions tocontrol this process. In another embodiment, the second manufacturingunit may be configured not to turn it upside down. In this case, thesecond manufacturing unit is configured to perform each step with thesecond sheet product being held in a reversed state (with the releasefilm facing upward), unlike the usual state, and to bond the secondsheet product to the lower side of the substrate W1. When the bonding isperformed so that the polarizing plate of the second sheet product canbe in 90° relation (crossed Nicol relation) to the polarizing plate ofthe first sheet product, the substrate W is turned by 90°, and then thesecond sheet product is bonded thereto. In the second manufacturing unitfor the respective steps, the mounting means, the feeding means, thethird release film removing means, the defect inspecting means, thefourth release film bonding means, and the cutting means are the same asthe corresponding means of the first manufacturing unit, and therefore,the description thereof is omitted.

The first and second control means control the means for the respectivesteps so that they can be synchronized. The timing of the operation ofeach means is calculated by a method using sensors placed at specificlocations or by a method of detecting the rotating part of the feedingmechanism with a rotary encoder or the like. The first and secondcontrol means may be implemented in cooperation with software programsand hardware resources such as CPU and memories. In this case, programsoftware, procedures, various settings, and so on are previously storedin memories. Private circuits, firmware, or the like may also be usedfor the implementation.

Other Embodiments

In the above embodiments, defect-containing sheet products are bonded totemporary units and collected. Alternatively, such products may bebonded to a belt-shaped separator so that they can be collected in theform of a roll.

The defect inspection may be performed using known defect inspectionmethods. Examples of defect inspection methods include inspection withautomatic inspection equipment and visual inspection by a checker.Automatic inspection equipment includes a system to automaticallyinspect defects (also referred to as flaws) in the sheet product, whichperforms a process including applying light to the product, capturingthe reflected-light image or the transmitted-light image through animaging unit such as a line sensor or a two-dimensional TV camera, anddetecting defects based on the captured image data. The image data arealso captured through a polarizing filter placed for inspection in theoptical path between the light source and the imaging unit. In general,the polarization axis (e.g., polarized light absorption axis) of thepolarizing filter for inspection is placed so as to be orthogonal(crossed-Nicol) to the polarization axis (e.g., polarized lightabsorption axis) of the polarizing plate (the test object). In thecrossed-Nicol configuration, no defect allows a full black image to beinput from the imaging unit, while any defect portion is detected asbeing not black (observed as a bright spot). Therefore, if anappropriate threshold is determined, defects can be detected. In suchbright spot detection, defects such as surface deposits and internalforeign matter are detected as bright spots. Besides the bright spotdetection, a method including capturing the transmitted-light image ofthe object with CCD and analyzing the image to detect foreign matter isalso applicable. In addition, a method including capturing thereflected-light image of the object with CCD and analyzing the image todetect foreign matter deposited on the surface is also applicable.

Example 1

A connected sheet product and an optical display unit were manufacturedusing the above connecting method. The sheet product is a laminatedstructure composed of a surface protecting film (PET film), an acrylicpressure-sensitive adhesive layer, a polarizing plate, an acrylicpressure-sensitive adhesive layer, and a release film (a PET film havinga silicone-treated surface to be laminated). The polarizing plateincludes a stretched and dyed polyvinyl alcohol film polarizer andtriacetylcellulose films provided on both sides of the polarizer with anadhesive interposed therebetween. The connecting member used is anadhesive tape (Dunplon Tape No. 3041 manufactured by Nitto DenkoCorporation). The adhesive tape has a width of 10 cm, a thickness of 70μm, an adhesive strength of 7 N/25 mm, a tensile strength of 120 N/25mm, and an elongation percentage of 140%. Various test methods are thesame as those described above. As shown in FIG. 1, the sheet productswere connected to each other with the connecting members. As a result,the two sheet products were successfully connected without breaking atthe connected portion, and the release films were smoothly andsuccessfully peeled off without interference with the other constituentmembers. As a result, the sheet product was successfully bonded to aliquid crystal cell substrate. The adhering force (A) between one of theadhesive tapes and the release film (a PTE film with a silicone-treatedsurface to be laminated) of the second sheet product was 3.5 N/25 mm.The adhering force (B) between the release film (a PTE film with asilicone-treated surface to be laminated) of the second sheet productand the pressure-sensitive adhesive layer was 0.02 N/25 mm. The adheringforce (C) between the other adhesive tape and the surface protectingfilm (PET film) of the second sheet product was 3.5 N/25 mm. Therefore,the relation C≧A>B (formula 1) was satisfied.

Example 2

The connecting method of Example 2 is shown in FIG. 3. The structure ofthe sheet product is the same as in Example 1. The end faces of thefirst and second sheet products were opposed to each other, and a heatsealing tool was pressed against both surfaces of the portion where thesheet products were opposed to each other, so that the surface portions501 and 502 of the sheets in contact with the tool were each subjectedto heat fusion. The tool was then removed, and each thermally-fusedportion was solidified, so that the sheets were connected to each other.In the resulting connected sheet product, the two sheet products weresuccessfully connected without breaking at the connected portion,although the mechanical strength of the connected portion was slightlylower than that in Example 1. The release films were smoothly andsuccessfully peeled off without interference with the other constituentmembers, and the resulting sheet product was successfully bonded to aliquid crystal cell substrate.

Optical Member

Examples of the polarizer and films generally include the materialsdescribed below, although some examples are described above with respectto the polarizer as a component of the optical member and films used onone or both sides of the polarizer.

Polarizer

The processes of dyeing, crosslinking and stretching a polyvinyl alcoholfilm are not necessarily independently performed and may be performed atthe same time or in any order. The polyvinyl alcohol film may besubjected to a swelling process before use. The process may generallyinclude the steps of immersing the polyvinyl alcohol film in a solutioncontaining iodine or a dichroic dye so that the film is dyed with theiodine or the dichroic dye being adsorbed thereto, then washing thefilm, uniaxially stretching the film to 3 to 7 times in a solutioncontaining boric acid, borax or the like, and then drying the film. Itis particularly preferred that the step of stretching the film in asolution containing iodine or a dichroic dye should be followed by thesteps of further stretching the film in a solution containing boricacid, borax or the like (two-stage stretching) and then drying the film,so that the iodine can be highly oriented to provide good polarizingproperties.

For example, the polyvinyl alcohol polymer may be a polymer produced bypolymerizing vinyl acetate and then saponifying the polymer or acopolymer produced by copolymerizing vinyl acetate with a small amountof a copolymerizable monomer such as an unsaturated carboxylic acid, anunsaturated sulfonic acid, or a cationic monomer. The averagepolymerization degree of the polyvinyl alcohol polymer is preferably,but not limited to, 1,000 or more, more preferably from 2,000 to 5,000.The saponification degree of the polyvinyl alcohol polymer is preferably85% by mole or more, more preferably from 98 to 100% by mole.

The thickness of the produced polarizer is generally, but not limitedto, from 5 to 80 μm. The thickness of the polarizer may be controlled byany conventional method such as tentering, roll stretching, or rolling.

As a non-limiting example, the polarizer and a polarizer-protectingtransparent film serving as a protective layer may be bonded to eachother with an adhesive such as an adhesive including a vinyl alcoholpolymer or an adhesive including a vinyl alcohol polymer and awater-soluble crosslinking agent therefor such as boric acid, borax,glutaraldehyde, melamine, or oxalic acid. The adhesive layer may beformed by applying and drying an aqueous solution layer. In the processof preparing the aqueous solution, if necessary, any other additive or acatalyst such as an acid may also be added.

Polarizer Protecting Film

Any appropriate transparent film may be used as the polarizer protectingfilm to be placed one or both sides of the polarizer. For example,thermoplastic reins with a high level of transparency, mechanicalstrength, thermal stability, water-blocking performance, isotropy, orthe like may be used. Examples of such thermoplastic resins includecellulose resins such as triacetylcellulose, polyester resins,polyethersulfone resins, polysulfone resins, polycarbonate resins,polyamide resins, polyimide resins, polyolefin resins, (meth)acrylicresins, cyclic polyolefin resins (norbornene resins), polyarylateresins, polystyrene resins, polyvinyl alcohol resins, and any blendthereof. While a transparent protective film may be bonded to one sideof the polarizer with an adhesive layer, a thermosetting resin or anultraviolet-curable resin such as a (meth)acrylic, urethane, acrylicurethane, epoxy, or silicone resin may be used to form a transparentprotective film on the other side of the polarizer. The transparentprotective film may contain any one or more appropriate additives.Examples of such an additive include an ultraviolet absorbing agent, anantioxidant, a lubricant, a plasticizer, a release agent, ananti-discoloration agent, a flame retardant, a nucleating agent, anantistatic agent, a pigment, and a colorant. The content of thethermoplastic resin in the transparent protective film is preferablyfrom 50 to 100% by weight, more preferably from 50 to 99% by weight,even more preferably from 60 to 98% by weight, in particular, preferablyfrom 70 to 97% by weight. If the content of the thermoplastic resin inthe transparent protective film is less than 50% by weight, hightransparency and other properties inherent in the thermoplastic resinmay be insufficiently exhibited. Amorphous PO films, cycloolefin polymer(COP) films, Arton films (manufactured by JSR Corporation), Zeonor films(manufactured by Zeon Corporation), and so on may also be used.

The polymer film described in JP-A No. 2001-343529 (WO01/37007) may alsobe used, for example, which comprises a resin composition containing (A)a thermoplastic resin having a substituted and/or unsubstituted imidegroup in the side chain and (B) a thermoplastic resin having asubstituted and/or unsubstituted phenyl and nitrile groups in the sidechain. Specifically, the film comprises a resin composition containingan alternating copolymer of isobutylene and N-methylmaleimide and anacrylonitrile-styrene copolymer. The film may be produced bymixing-extrusion of the resin composition. These films have a low levelof retardation and photoelastic coefficient and thus can preventpolarizing plates from having defects such as strain-induced unevenness.They also have low water-vapor permeability and thus have high humidityresistance.

The thickness of the transparent protective film is generally from about1 to about 500 μm, in particular, preferably from 1 to 300 μm, morepreferably from 5 to 200 μm, in view of strength, workability such ashandleability, thin layer formability, or the like, while it may bedetermined as needed. A transparent protective film with a thickness of5 to 150 μm is particularly preferred.

For practical use, the optical film may also have a multilayeredstructure in which various optical layers are laminated. Examples ofsuch optical layers include, but are not limited to, layers formed byperforming hard coating treatment, antireflection treatment, or surfacetreatment for anti-sticking, diffusion or antiglare purpose on thetransparent protective film surface to which no polarizer will be bonded(the surface on which the adhesive coating layer is not provided), andoriented liquid crystal layers for viewing angle compensation or otherpurposes. An optical film(s) for use in forming a liquid crystal displayor the like, such as a reflector, a transflector, a retardation plate(including a wavelength plate (λ plate) such as a half or quarterwavelength plate), or a viewing angle compensation film may also be usedin the form of a layer or a laminate of two or more layers.

Retardation Plate

An example of the optical film to be placed on the polarizer includes aretardation plate. Examples of the retardation plate includebirefringent films produced by uniaxially or biaxially stretchingpolymer materials, oriented liquid crystal polymer films, and orientedliquid crystal polymer layers supported on films. The stretching processmay be typically performed by roll stretching, long-gap stretching,tenter stretching, or tubular stretching. Uniaxial stretching isgenerally performed to a stretch ratio of about 1.1 to about 3. Thethickness of the retardation plate is generally, but not limited to,from 10 to 200 μm, preferably from 20 to 100 μm.

Examples of the polymer materials include polyvinyl alcohol, polyvinylbutyral, poly(methyl vinyl ether), poly(hydroxyethyl acrylate),hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose,polycarbonate, polyarylate, polysulfone, polyethylene terephthalate,polyethylene naphthalate, polyethersulfone, polyphenylene sulfide,polyphenylene oxide, polyallylsulfone, polyvinyl alcohol, polyamide,polyimide, polyolefin, polyvinyl chloride, cellulose polymers, andvarious types of binary or ternary copolymers thereof, graft copolymersthereof, and any blend thereof. Any of these polymer materials may beformed into an oriented product (a stretched film) by stretching or thelike.

Viewing Angle Compensation Film

Another example of the optical film to be placed on the polarizerincludes a viewing angle compensation film. The viewing anglecompensation film is for expanding the viewing angle so that images canbe relatively clearly viewed even when the screen of a liquid crystaldisplay is viewed from directions not perpendicular but somewhat obliqueto the screen. Examples of such a viewing angle compensation retardationplate include a retardation film, an oriented film of a liquid crystalpolymer or the like, and an oriented layer of a liquid crystal polymeror the like supported on a transparent substrate. General retardationplates are produced with a polymer film that is uniaxially stretched inthe in-plane direction and has birefringence. On the other hand,retardation plates for use as the viewing angle compensation film areproduced with a bi-directionally stretched film such as a polymer filmthat is biaxially stretched in the in-plane direction and hasbirefringence, a polymer film that is uniaxially stretched in thein-plane direction and also stretched in the thickness direction so thatit has a controlled refractive index in the thickness direction and hasbirefringence, and an obliquely oriented film. Examples of the obliquelyoriented film include a film produced by a process including bonding aheat-shrinkable film to a polymer film and stretching and/or shrinkingthe polymer film under the action of the heat-shrinkage force, and anobliquely-oriented liquid crystal polymer film. The raw material polymerfor the retardation plate may be the same as the polymer described abovefor the retardation plate, and any appropriate polymer may be useddepending on the purpose such as prevention of coloration caused bychanges in viewing angle based on the retardation of a liquid crystalcell and expansion of the viewing angle at which good visibility isachieved.

In order to expand the viewing angle at which good visibility isachieved, an optical compensation retardation plate is preferably used,which includes a triacetylcellulose film and an optically-anisotropiclayer of an oriented liquid crystal polymer, specifically anobliquely-oriented discotic liquid crystal polymer layer, supported onthe film.

Brightness Enhancement Film

A laminate of a polarizing plate and a brightness enhancement film isgenerally placed on the back side of a liquid crystal cell, when used.The brightness enhancement film exhibits the property that when light isincident on it from a backlight of a liquid crystal display or the likeor when natural light is reflected from the back side and incident onit, it reflects linearly polarized light with a specific polarizationaxis or reflects circularly polarized light in a specific direction andtransmits the other part of the light. When light from a light sourcesuch as a backlight is incident on a laminate of a polarizing plate anda brightness enhancement film, transmitted light in a specificpolarization state is produced, and light in the state other than thespecific polarization sate is not transmitted but reflected. The lightreflected from the surface of the brightness enhancement film may bereversed by a reflective layer or the like provided behind thebrightness enhancement film and allowed to reenter the brightnessenhancement film so that the light can be entirely or partiallytransmitted in the specific polarization state. In this case, thequantity of the light transmitted through the brightness enhancementfilm can be increased, and polarized light, which is less likely to beabsorbed by the polarizer, can be supplied so that the brightness can beenhanced by increasing the quantity of the light available at a liquidcrystal image display or the like.

Examples of the brightness enhancement film that may be used include afilm having the property of transmitting linearly polarized light with aspecific polarization axis and reflecting the other type of light, suchas a dielectric multilayer thin film or a multilayer laminate of thinfilms different in refractive index anisotropy, and a film having theproperty of reflecting one of clockwise circularly polarized light andcounterclockwise circularly polarized light and transmitting the other,such as an oriented cholesteric liquid crystal polymer film or anoriented cholesteric liquid crystal layer supported on a film substrate.

Pressure-Sensitive Adhesive

In an embodiment of the invention, the polarizing plate or the opticalmember is provided with a pressure-sensitive adhesive layer for bondingit to another component such as a liquid crystal cell. Thepressure-sensitive adhesive layer may be formed of any appropriatepressure-sensitive adhesive such as an acrylic pressure-sensitiveadhesive according to conventional techniques. The pressure-sensitiveadhesive layer preferably has low moisture absorption coefficient andhigh heat resistance, in order to prevent moisture absorption-inducedfoaming or peeling, to prevent optical property degradation due to athermal expansion difference or the like, to prevent warping of a liquidcrystal cell, and to form an image display with high quality and highdurability. The pressure-sensitive adhesive layer may also contain fineparticles so as to have light diffusing properties. Thepressure-sensitive adhesive layer may be provided as needed on anecessary surface. Concerning a polarizing plate comprising a polarizerand a polarizer protecting film layer, for example, a pressure-sensitiveadhesive layer may be provided as needed on one or both sides of thepolarizer protecting layer.

Release Film

The exposed surface of the pressure-sensitive adhesive layer may betemporarily covered with a release film (it may also called “separator”)for antifouling or the like until it is put to use. This can preventcontact with the pressure-sensitive adhesive layer during usualhandling. A conventional appropriate separator may be used, such as anappropriate thin leave including a plastic film, a rubber sheet, a papersheet, a cloth, a nonwoven fabric, a net, a foam sheet, a metal leaf, ora laminate thereof, which is optionally coated with any appropriaterelease agent such as a silicone, long-chain alkyl or fluoride releaseagent, or molybdenum sulfide.

Surface Protecting Member

A surface protecting member may be provided on the opposite side of theoptical member from the side where the separator is provided. A surfaceprotecting film may be formed as the surface protecting member through aweak pressure-sensitive adhesive. The main purpose thereof isanti-scratch, anti-fouling, or the like. For example, the surfaceprotecting film may be a single layer of a plastic film or a laminate ofplastic film layers. Examples of the surface protecting member includean appropriate thin leave such as a plastic film, a rubber sheet, apaper sheet, a cloth, a nonwoven fabric, a net, a foam sheet, a metalleaf, or a laminate thereof, which is optionally coated with anyappropriate release agent such as a silicone, long-chain alkyl orfluoride release agent, or molybdenum sulfide.

In an embodiment of the invention, an ultraviolet absorbing capabilitymay be imparted to the polarizer, the polarizer protecting film, or anyother film such as the surface protecting film or the release film, oreach layer such as the pressure-sensitive adhesive, for example, bytreatment with an ultraviolet-absorbing agent such as a salicylate estercompound, a benzophenol compound, a benzotriazole compound, acyanoacrylate compound, or a nickel complex salt compound.

Optical Image Display

In an embodiment of the invention, the optical member is preferably usedto form an image display such as a liquid crystal display, an organicelectroluminescence display (organic EL display) or a plasma displaypanel (PDP).

In an embodiment of the invention, the optical member is preferably usedto form any of various devices such as liquid crystal displays. Liquidcrystal displays may be formed according to conventional techniques.Specifically, a liquid crystal display may be typically formed byassembling a liquid crystal cell and optical films, and optionalcomponents such as a lighting system and by incorporating a drivingcircuit according to conventional techniques, except that the opticalfilm is used according to the invention. Any type of liquid crystal cellsuch as TN type, STN type or n type may be used.

1. A process for production of a connected sheet product including sheetproducts that are connected to one another and each have at least anoptical member and a release film provided on one side of the opticalmember with a pressure-sensitive adhesive interposed therebetween,comprising: opposing a transverse end face of a first sheet product to atransverse end face of a second sheet product; connecting release filmsof the first and second sheet products with a connecting member; andconnecting surface members of the first and second sheet products with aconnecting member on the opposite side from the release films.
 2. Aconnected sheet product, comprising: first and second sheet productsthat are connected to each other and each have at least an opticalmember and a release film provided on one side of the optical memberwith a pressure-sensitive adhesive interposed therebetween, wherein atransverse end face of the first sheet product and a transverse end faceof the second sheet product are opposed to each other; a connectingmember with which the release films of the first and second sheetproducts are connected to each other; and another connecting member withwhich surface members of the first and second sheet products areconnected to each other on the opposite side from the release films. 3.A process for production of an optical display unit, comprising: acutting step comprising cutting the connected sheet product manufacturedby the method of claim 1 with exception of a release film into a piecewith a predetermined size by cutting means; and a bonding stepcomprising bonding the piece with the predetermined size to a substratewith the pressure-sensitive adhesive interposed therebetween whileremoving the release film.
 4. A process for production of an opticaldisplay unit, comprising: a cutting step comprising cutting theconnected sheet product of claim 2 with exception of a release film intoa piece with a predetermined size by cutting means; and a bonding stepcomprising bonding the piece with the predetermined size to a substratewith the pressure-sensitive adhesive interposed therebetween whileremoving the release film.